1. Field of the Invention
The present invention relates to a particle beam irradiation system for accurately irradiating the affected area of a patient with a particle beam such as a proton beam, a heavy ion beam, or the like, or more particularly to a particle beam irradiation system having a particle beam irradiation apparatus which is free of a rotating gantry structure and which radiates a particle beam from one direction, so that the particle beam irradiation system can be reduced in overall size and cost, and the particle beam irradiation apparatus has its accuracy control made easy. The particle beam irradiation system according to an embodiment of the present invention has a unit structure housing a CT scanner and a drive unit in integral combination, the CT scanner being installed in a treatment chamber for accurately confirming the position of the affected area of the patient and the drive unit being integrally combined with the CT scanner for moving the patient from the CT scanner to a particle beam irradiation range. For treating the patient with the particle beam irradiation system, the particle beam irradiation system employs a fixing device for fixing the patient to the drive unit, the fixing device being rotatable about the craniocaudal axis of the patient which is being fixed to the drive unit by the fixing device. Accordingly, the present invention is concerned with a particle beam irradiation system for setting the patient's body to any of various angles, detecting the affected area of the patient with a CT scanner, and moving a drive unit while the patient is being held in a set posture, for thereby accurately bringing the affected area of the patient into a particle beam applying position. The particle beam irradiation system according to an embodiment of the present invention has a unit structure housing a CT scanner and a drive unit in integral combination, the unit structure being rotatable about an axis perpendicular to a plane which includes both the direction in which the particle beam is applied and the direction which the drive unit moves, while the patient is being held in a constant posture. Consequently, the present invention relates to a particle beam irradiation system for accurately aiming at the affected area of the patient from many directions in a three-dimensional space with respect to one direction in which the particle beam is applied.
2. Description of the Related Art
Heretofore, there has been known a process of treating a cancer or the like by irradiating the affected area of the patient with a particle beam (ion beam) such as a proton beam, a heavy ion beam, or the like. The particle radiation therapy is capable of applying a lower radiation dose to a normal tissue than the radiation therapy in the past based on a peculiar dose distribution of the particle beam. For further reducing a redundant radiation dose of the radiation beam applied to a normal tissue, there has been employed a rotary gantry structure for applying the particle beam at an appropriate angle to the patient's body (multiple field irradiation). For example, Japanese Patent Laid-open No. 2006-218315 (hereinafter referred to as Patent Document 1) discloses a medical particle beam irradiation apparatus including a charged particle beam generator having an ion source, a preaccelerator, and a synchrotron, and a rotary gantry. Japanese Patent Laid-open No. 2003-190304 discloses a particle beam treatment apparatus for treating the affected area of a patient by irradiating it with a charged particle beam such as a proton beam, a heavy ion beam, or the like. The disclosed particle beam treatment apparatus has a treatment table for placing the patient thereon, the treatment table having a top plate with a recess defined therein. When the patient on the treatment table is irradiated with the particle beam applied from below by a rotary gantry, the particle beam is directly applied to the patient's body through the recess, not through the top plate.
Japanese Patent laid-open No. Hei 9-192244 (hereinafter referred to as Patent Document 3) reveals a particle beam irradiation apparatus having a particle beam generating means for generating a particle beam such as a proton beam, a particle beam circularly accelerating means for applying a magnetic field to the generated particle beam to emit the particle beam which has been rotated in a circular pattern and accelerated, a beam transporting means for transporting the particle beam to an irradiation chamber where an object to be irradiated is placed, an irradiation field forming means for shaping the particle beam into a desired shape and applying the shaped particle beam to the object, and a rotating means for rotating the particle beam circularly accelerating means, the beam transporting means, and the irradiation field forming means in unison with each other. The particle beam circularly accelerating means has an acceleration trajectory plane lying perpendicularly to the axis of rotation of the rotating means. The object to be irradiated with the particle beam is disposed on the axis of rotation of the rotating means. Patent Document 3 also discloses a rotary particle beam irradiation apparatus in the past having a cyclotron as a particle beam circularly accelerating means for generating a particle beam such as a proton beam and accelerating the particle beam to a high energy level, a quadrupole electromagnet for focusing the particle beam, which is a cluster of particles, into a desired shape, a deflection electromagnet for deflecting the particle beam, a directional control electromagnet for changing the direction in which the particle beam is transported, and a rotary particle beam irradiation table assembly for applying the particle beam to a target which is a cancer patient. The rotary particle beam irradiation table assembly includes a treatment table disposed at the rotational center, a beam transporting means for deflecting the particle beam at a right angle and guiding the particle beam between a pair of rotating frames in order to apply the particle beam perpendicularly to the target placed on the treatment table, and an irradiation field forming means for forming an irradiation field in alignment with the target. A counterweight is attached to the rotary frames to keep them in balance. The rotary frames are rotatably supported on rollers. The target on the treatment table is irradiated with the radiation beam while the rotary frames are being rotated by a rotational drive unit.
However, it is much more technically challenging, takes up a larger space, requires a more tedious and time-consuming accuracy control task, and is much more costly to construct a rotary gantry structure which incorporates an apparatus for applying a proton beam or a heavy ion beam than an apparatus for applying an X-ray. Even a proton beam or a heavy ion beam is not effective enough if applied to the patient in one direction only. Therefore, for better therapeutic results, it is desirable to be able to apply the particle beam at any desired angle for multiple-direction irradiation (multiple field irradiation). Furthermore, it is necessary that the particle beam be applied in highly accurate alignment with the position of the patient.